1. Field of the Invention
The present invention relates to an engine with an inclined cylinder, particularly relates to an engine with the inclined cylinder and two balancer shafts.
2. Description of the Prior Art
In the engine, total height of the engine can be suppressed to be low by inclining and arranging the cylinder. In addition, by providing the two balancer shafts, inertia force generated by reciprocal motion of a piston and rotation of a crankshaft can be completely eliminated as far as possible, and vibration of the engine can be suppressed.
FIG. 21 shows an engine described in Japanese Patent Laid-Open Application No. 2000-88057. The engine has a single cylinder 100, and a center line C1 of the cylinder 100 is inclined by a fixed angle relative to a vertical line M intersecting with an axis O0 of a crankshaft 103. In a crankcase 101, the crankshaft 103 is substantially horizontally-disposed, and two balancer shafts 105, 106 are arranged substantially in parallel to the crankshaft 103. In the crankcase 101, a cam shaft 111 and a governor shaft 112 are also arranged, and the cam shaft 111 is arranged on the same axis O1 as the one balancer shaft 105.
The substantially entire one balancer shaft 105 including a weight portion 105a is arranged so as to be positioned on the side of the cylinder 100 relative to the entire crankshaft 103 (including journal portions, crank arms, a crank pin, and a weight portion). The substantially entire other balancer shaft 106 including a weight portion 106a and the like is arranged so as to be positioned on the opposite side of the cylinder 100 relative to the entire crankshaft 103.
The one balancer shaft 105 is interlocked and coupled to the crankshaft 103 via a chain transmission mechanism including a driven sprocket 115, a chain 116, and a drive sprocket 117, and rotated in the same direction as the rotation direction A1 of the crankshaft 103 at the same rotation speed. The other balancer shaft 106 is interlocked and coupled to the crankshaft 103 via a gear transmission mechanism including a driven gear 118 and a drive gear 119, and rotated in the opposite direction to the rotation direction A1 of the crankshaft 103 at the same rotation speed.
In the engine with the inclined cylinder shown in FIG. 21, total height of the engine can be lowered. However, size in the front and rear direction (arrow H) of the crankcase 101, that is, size in the horizontal direction orthogonal to the crankshaft 103 is elongated. Thus, enlargement of the entire engine cannot be avoided. Particularly, in order to accommodate the other balancer shaft 106 arranged on the opposite side of the cylinder 100 and the driven gear 118, a part 101a protruding into a large arc shape on the opposite side of the cylinder is formed in an end wall 101a of the crankcase 101, and the part is a cause for the enlargement of the engine.
An object of the present invention is to completely eliminate inertia force generated by reciprocal motion of a piston and rotation of a crankshaft as far as possible in an engine with an inclined cylinder by providing two balancer shafts, and suppress vibration of the engine. Further, another object of the invention is to, although the two balancer shafts are provided, decrease size in the horizontal direction (size in the front and rear direction) of a crankcase by devising arrangement of the two balancer shafts.